Table 2 Quality assessment of included studies ¹

Chang et al. 2012 [19]

***

**

***

8

Chung et al. 2008 [20]

***

*

**

6

Hsieh et al. 2012 [23]

***

**

***

8

Koro et al. 2007 [24]

***

*

**

6

Vinikoor et al. 2009 [26]

**

*

**

5

Wong et al. 2012 [27]

***

**

**

7

Yang et al. 2004 [28]

***

**

**

7

Author

Quality assessment criteria—Cohort

Selection

Comparability

Outcome/Exposure

Overall quality

Campbell et al. 2010 [17]

**

**

***

7

Carstensen et al. 2012 [18]

***

**

***

8

Currie et al. 2009 [21]

**

**

**

6

Gu et al. 2013 [22]

***

**

***

8

Onitilo et al. 2013 [25]

**

**

**

6